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All About Opals: Fascinating Facts About This Gem

Karin Jacobson gem news opals

One of my favorite things about making jewelry is getting to work with all kinds of fascinating gemstones. They are incredibly beautiful, but they are also incredibly interesting. Today, I want to share a little bit about  opals - a marvelously varied and mesmerizing stone that I love using in my jewelry designs! This will be Opals 101, just the basics, since this ancient mineral compound has a long history. But I hope to hit most of the highlights, including how to keep YOUR opals healthy and strong.

What is an opal?

The answer to this question makes the amateur geologist in me so happy! Opal is a non-crystalline form of the mineral silica. So unlike its cousins quartz and agate which are comprised of geometric crystals, opals are made up of silica lumps. That’s right, lumps are what give these stones their amorphous, glistening appearance![1]

The other main ingredient in opal is water. The stone is formed when water runs through the earth, gathers bits of silica from naturally occurring sandstone, and routes this silica-infused solution through cracks in the stone below made by faults or decomposing fossils. When the water evaporates, it leaves behind a lumpy silica deposit. When this cycle repeats over very long periods of time, an opal is formed.[2] “Very long periods of time” is not an exaggeration: Most of the opals we mine were made between 65 million and 145 million years ago. They show up in the Cretaceous layer of rock, which was created when dinosaurs roamed the earth.[3]

And speaking of dinosaurs … here’s an interesting tidbit for you: some of my opals, like the ones in the earrings and necklace below, were cut by Loren Gurche - a PhD student in paleontology at the University of Kansas who has also been working on a news-making dig in western North Dakota, which is believed to have fossils from the very day the asteroid that killed the dinosaurs hit the earth and ended the Cretaceous period.

On the right are Coober Pedy opals in my Fire & Forge earrings, and on the left is a Lightning Ridge opal - both cut by Loren Gurche of Ancients17.

Where do opals come from and how do we mine them?

The conditions needed to form opals only occurred in certain parts of the world millions of years ago, which means that they show up in a few discrete pockets. In fact, more than 90% of the world’s opals come from Southern Australia, and all black opals come from Australia. (More on opal types shortly!) Opals are also mined in Ethiopia, Brazil, Mexico, Czechoslovakia, and parts of Nevada & Oregon.[4]

Since they’re formed when water and silica mix, opal is usually found near the earth’s surface in areas where ancient geothermal hot springs were once actively bubbling away. This means that the mining process isn’t as tricky or destructive as it is for some other gems. It also has some very descriptive terminology, including “noodling” and “rumbling.” (Leave it to the Aussies to coin such fantastic words for opal mining!)

In most cases, miners will create a shaft in the earth with a pick and shovel, digging down until some promising “opal dirt” is found. The shaft could be as short as 10 feet or as long as 65 feet. Since the stone is delicate, miners will then use a handpick or screwdriver to extract any opals they find. However, if miners have a big heap of opal dirt to pick through, they’ll start “noodling,” picking through the loose earth by hand or using a rake and sieve for tools. “Rumbling” takes place when dirt believed to contain opals is processed through a mesh-lined drum to separate out the stones.[5] It’s a finicky process, but can lead to the discovery of gorgeous deposits of this precious mineral.

What’s the difference between opal types?

There are dozens of varieties of opals, including ones that have been altered to make them more stable or easier to manipulate. Here are a few of the types I’ve used in my own designs:

  • Black opal: Only found in Australia, has a dark and rich tone. These are the most valuable of the opal types.
  • White opal: Paler in tone than black opal and usually less valuable, but still very lovely! They can be milky in appearance, but with flecks of bright color - and the finer ones really capture the rainbow.
  • Boulder opal: This is an opal that includes a bit of the rock from which it’s been cut, often ironstone. This makes the stone appear dark and rich, and also sometimes shows off the way that the opal formed in a crack in the rock, like in this pendant.
  • Jelly opal: Most opals appear to have flat flecks of color, but jelly opals look more liquid. Like jelly!
  • Fire opal: Typically found in Mexico, this is any opal with a red or orange appearance.
Clockwise from top left: Origami pendant with Australian black opal; Australian boulder opal pendant; pearl earrings with Mexican fire opals (pear shaped & faceted); pendant with pear shaped Ethiopian jelly opal. (And for an example of a white opal, check out the Coober Pedy opals in the previous photo.)

As I mentioned, opals are fairly soft and delicate stones, so jewelers have some techniques to keep them stable. A solid opal is opal through and through, but many set opals are called doublets, which means there’s a slice of opal adhered to a layer of onyx or other dark stone. This both darkens the appearance of the opal itself, and gives it more stability.[6]

All of these pieces were made with opal doublets - you can see that they're generally darker than solid opal, but still full of color and life!

How do I keep my opals looking fabulous?

First off, don’t worry! You’re not going to destroy your opal jewelry just by wearing it. These stones are most beautiful when allowed to catch natural light, so be sure to keep your pieces in heavy rotation.

However, there are a few things you can do to make sure your opal pieces stay in great shape for years to come. Most importantly, don’t wear them when doing any sort of manual labor; gardening, dishes, bare-knuckle boxing, stone masonry, etc. They can scratch and break, so keep them clear of sharp and hard objects. Next, if your opals are doublets don’t soak them in water. Since they’re opals adhered to other gems, the adhesive can be eroded by too much exposure to water! Clean your opals gently with mild detergent in warm water and a soft toothbrush or cloth. Don’t use bleach, chemicals, or ultrasonic cleaners. Finally, if you need to store your opals for a long period, just wrap them in cloth or a padded bag and stash them away.

I loved working with opals for the Fire & Facets show last year at Gill Wing Jewellery in London and for Fire & Forge at Vincent’s Fine Jewelry in 2017, and continue to enjoy working this lovely and mysterious stone into my designs. Interested in commissioning an opal piece for yourself? Reach out and let’s discuss!


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